Did you save the design before exporting to Repetier Host ?
That might be the reasion.
Also, making components from bodies can be done as in your case, but it's not a good practice.
If you add any other parts to your design, you are better off following Fusion 360 R.U.L.E #1: Before doing anything, create a component and make sure it's activated.
- All objects created after activation such as sketches, bodies, construction geometry etc. are created in that component.
- When activating a component the timeline will be filtered to show only this itmes that pertain to that component, which wil working with a multi part design with a long timeline much easier.